Spinal fixation is a well known and frequently used medical procedure. Pedicle, lateral, and oblique mounting devices may be used to secure corrective spinal instrumentation to a portion of the spine that has been selected to be fused by arthrodesis. Fixation of the skull to the cervical spine may be used to treat trauma to the neck, degenerative diseases such as rheumatoid arthritis, and congenital instability. Many current implantable devices designed to immobilize the skull with respect to the upper cervical spine are assemblies of several components which are not designed specifically for fusing the cervical spine to the skull, but instead are assembled from multiple components designed for other applications. Such assembly may prolong and complicate the implantation procedure.
A typical spinal fixation system includes corrective spinal instrumentation that is attached to selected vertebrae of the spine by screws, hooks, and clamps. Various types of screws, hooks, and clamps have been used for attaching such corrective spinal instrumentation to selected portions of a patient's spine. Examples of pedicle screws and other types of attachments are illustrated in U.S. Pat. Nos. 4,763,644; 4,805,602; 4,887,596; 4,950,269; and 5,129,388. Each of these patents is incorporated by reference as if fully set forth herein. Examples of such multipart spinal fixation systems include U.S. Pat. Nos. 5,360,429 and 5,542,946, the disclosure of each of which is incorporated by reference.
With respect to occipital-to-cervical spinal fixation systems, contoured loop and wire constructs, rod constructs, rod and plate constructs and pre-contoured “U-loop”-type constructs have been used. An example of such a device is the OMI “U loop” device manufactured by Ohio Medical Instruments. However, such devices have a number of limitations, including the lack of appropriately sized loops for children under five years of age; the extensive modification and bending of the loops required during surgery, which can lead to failure of the device even before installation; cumbersome methods of coupling the devices to the anchor screws; and the lack of an option for installing a posterior cervical screw, which can be an urgent need for patients with missing lamina or inadequate laminar bone quality.
With these multi-piece systems, a number of problems may occur. For example, pressure necrosis may occur at the points of hook or wire fixation, leading to failure. Supplementation of such systems with halo vests often then fails to prevent micro-motion leading to non-union of the arthrodesis. Additionally, the time for surgery may be extended by the need to build and install a multi-piece assembly from separate components.
A few occipital-cervical spinal fixation systems, such as that disclosed in U.S. Pat. No. 6,146,382, the disclosure of which is incorporated by reference herein, attempt to simplify the implantation of the system by reducing the number of parts. A single plate attaches to an attachment site on the skull, and arms extend down from the plate to the cervical vertebrae. The arms are coplanar with the plate and bend at the tips where a separate connection member is attached. The separate attachment member is then attached at the top surface of the C2 vertebra. A cable is then attached by a hook system to the plate to a vertebra posterior to the arms, in order to retain a bone graft material in place. The '382 device thus still includes a number of parts that are assembled in situ, retaining the issues described with multi-piece systems.
Approximately 500 surgical cases of pediatric occipito-cervical fusions are performed in North America each year on children suffering from occipital-cervical instability. Current occipital-cervical fixation devices, such as the '382 device, are designed for adults and are therefore typically too large for use in children. Additionally, as the relationship of a child's head to the body differs from that of an adult due to allometric growth, devices designed for adults may not sustain the correct relationship of the head and neck for children. Surgical concerns are magnified when treating children, due to their smaller physical size, the abnormal anatomy that may be caused by craniovertebral anomalies, and their growth potential.
Previously, graft/wire constructs were reported to be associated with a nonunion rate as high as 30% for C1-C2 fusion; however, this incidence improves considerably with the use of a halo orthosis. Transarticular screw placement creates immediate atlantoaxial joint stability and, in contrast to previous posterior wiring/graft constructs, does not require postsurgical brace therapy. However, such procedures require surgical precision because serious potential risks are associated with improper screw placement. Thus, many spine surgeons are reluctant to perform such a procedure.
Accordingly, an occipital-cervical spinal fixation system that operated as a single plate, not requiring the use of additional component plates, hooks or rods would be an improvement in the art. Such a system that is configured for use in children or small adults would be an additional improvement in the art.